The present invention relates to a metal laminate gasket installed between a cylinder head and a cylinder block of an internal combustion engine to seal therebetween.
Recently, because of improved technologies of an engine, the maximum explosion pressure tends to become high. Especially, in a diesel engine, the tendency of the high maximum explosion pressure is remarkable. On the other hand, because of a tendency of making the engines lighter, the mechanical strength tends to decline. As a result, a lift or upward movement of the cylinder head during the cylinder explosion increases, so that a following capability relative to the lift of the cylinder head gasket is required.
However, in a well-known metal laminate cylinder head gasket, especially, the metal laminate cylinder head gasket, which forms a first seal portion with a bead around a combustion chamber hole, has a smaller amount of compression of the original bead compared to the lift mentioned above. Accordingly, in order to assure the following capability relative to the increased lift, in addition to the existing first seal portion with a large total thickness of laminated metal plates around the combustion chamber hole, the well-known metal laminate cylinder head gasket is provided with a second seal portion with the following capability relative to the lift, wherein the total thickness of the laminated metal plates is smaller than that of the first seal portion, but the cylinder head is larger than that of the first seal portion, so that following capability is assured even when the cylinder head is widely lifted (refer to a Japanese Patent Publication (TOKKAI) No. 2006-207688).
Basically, it is preferred that the following capability relative to the lift of the cylinder head is assured at the first seal portion. In such a case, if there is a large difference in level between the first seal portion which has a large total thickness of the laminated metal plates and the second seal portion which has a total thickness of the laminated metal plates smaller than that of the first seal portion, a compression mark may remain in the cylinder head and/or the cylinder block due to the difference in the total thickness. As a result, the sealing quality of each seal portion may be significantly deteriorated.
This invention is made in order to solve the above-mentioned problems, and an object of the present invention is to provide a metal laminate gasket wherein the first seal portion around the combustion chamber hole can assure the following capability relative to the lift of the cylinder head in the cylinder explosion, and the difference in the total thickness of the seal portions around the combustion chamber hole is set in a stepwise fashion from the first seal portion through a third seal portion, so that an excellent sealing quality of the seal portions can be assured without any compression mark in the cylinder head and/or the cylinder block due to the difference in thickness.
Further objects and advantages of the invention will be apparent from the following description of the invention.